1. Field of the Invention
The present invention relates to a powered vehicle door closing system and specifically to a powered vehicle door closing system suitable for an automotive vehicle such as a van with a sliding door moveable between open and closed positions relative to a vehicle body opening, and more specifically to a system which is capable of forcibly and automatically moving a latch member employed in a lock unit from a half-latched position (a nearly-closed position of the sliding door) to a fully-latched position (a fully-closed position of the sliding door) by powering the final, low-displacement/high-force movement of the sliding door.
2. Description of the Prior Art
Recently, there have been proposed and developed various powered vehicle door closing systems which can automatically move a latch member from a half-latched position to a fully-latched position. One such powered vehicle door closing system has been disclosed in Japanese Patent Provisional Publication (Tokkai Heisei) No. 1-105886. The powered door closing system disclosed in the Japanese Patent Provisional Publication No. 1-105886 is applied to a door lock for an automobile sliding door. The prior art door closing system has three switches, namely a first switch for detection of a half-latched state of the latch member, a second switch for detection of a fully-latched state of the latch member, and a third member for detection of a stand-by position of a moveable drive lever (a portion of a force-transmitting linkage) by way of which the latch member can be shifted from the half-latched position to the fully-latched position. The first switch consists of a pair of electrical contacts, one being a stationary electrical contact provided in the vehicle body and the other being a spring-loaded, plunger-type electrical contact provided in the door for contact with the stationary contact upon shift to the half-latched position of the latch member via the manual door operation. The first switch is responsive to the movement of the sliding door in such a manner as to rotate the drive lever away from its stand-by position by way of normal rotation (positive rotation) of a drive motor such as a reversible electric motor when the sliding door reaches the half-latched position of the latch member, and as a result the latch member is forcibly moved to its fully-latched position. The second switch is responsive to the movement of the latch member in such a manner as to rotate the drive lever toward the stand-by position by way of reverse-rotation (negative rotation) of the drive motor when the latch member reaches the fully-latched position. The third switch is responsive to the movement of the drive lever in such a manner as to stop the drive motor and consequently to maintain the drive lever at the stand-by position immediately when the drive lever reaches the stand-by position. Each of the second and third switches consists of an ordinary limit switch. The conventional powered door closing system also includes a motor-drive controlling circuit disposed in the sliding door for properly controlling the drive motor depending upon detection results of the respective switches. In the Japanese Patent Provisional Publication No. 1-105886, the controlling circuit includes a plurality of relays to establish an electric power supply circuit to the drive motor in cooperation with two pairs of electric contacts. A basic structure of each electric contact pair is similar to the above-noted first switch. That is, the respective contact pair consists of a stationary electrical contact provided in the vehicle body and a spring-loaded plunger-type electrical contact provided onto the sliding door. The stationary contact of a first pair of the two electric contact pairs is connected to a positive terminal such as voltage +12, whereas the stationary contact of a second pair of the two electric contact pairs is connected to ground. The opposing electric contacts of the respective electric contact pair are brought into electric-contact with each other to establish the power supply circuit for the drive motor just before the half-latched position is reached during the manual door closing operation. In such a conventional powered vehicle door closing system, there is a possibility that the associated electrical contacts are accidentally temporarily disengaged from each other owing to vibrations of the vehicle. If the temporary disengagement occurs, the controlling circuit is usually reset. Thereafter, in the event that the associated contacts are engaged with each other once again, the drive motor will be driven again even when the latch member has already reached the fully-latched position. This produces a wasteful electric-power consumption. Additionally, when closing the sliding door rapidly with great momentum, the latch member may be often shifted to the fully-latched position owing to inertia of the door, without requiring any auto-closing action of the door closing system. Even when the latch member has already been shifted to the fully-latched position, the drive motor will be ineffectively driven with a response-time delay of the actual motor driving action with respect to a timing of detection of the half-latched position. The operator may feel uncomfortable.